Stilbenoids of Norway spruce bark: does the variability caused by raw-material processing offset the biological variability?

Abstract

Polyphenolic stilbene glucosides are abundant in the fresh bark of Norway spruce (Picea abies [L.] Karst.) trees. Stilbene-rich bark extracts could be industrially utilized as preservatives due to their antioxidative, antifungal, and antibacterial properties. The postharvesting conditions, especially industrial debarking, influence the chemical properties of bark. Inherent variation in high-value compounds of bark is assumed to be offset by modifications within the bark supply chain; however, essential quantitative information is still rare. This study elucidated the magnitude of variation in the stilbenoid content and composition of Norway spruce bark due to (1) the geographical origin of Norway spruce seeds, (2) the geographical location of the growing site, (3) within-tree variability, and (4) industrial handling and pilot-scale extraction and fractioning processes. The inherent variation in stilbenoid content was large: the total average stilbenoid content of the inner bark varied from 70 to 110 mg/g of dry weight (DW). Sampling position in the stem and growing site explained over 50% of the total variance in stilbenoid content. Trees with a northern origin of seeds had a higher isorhapontin/astringin ratio than the trees with a southern origin of seeds, regardless of their growing site. Industrial bark from sawmills showed a significantly higher total stilbenoid content in winter than in summer, 22 mg/g and 1–3 mg/g DW, respectively. The inherent variation in the stilbenoid content was offset by the variation caused by the debarking process and experimental pilot-scale processing. To optimize the yield of stilbenoids from spruce bark, sampling of northern forests and short handling times in the supply chain are recommended.